This question is fascinating because Canada/US relations at this time were among the first incidents of pan-Canadian national sentiment (as opposed to Imperial or Québécois nationalist sentiment) rising within the Dominion. The inciting point for my assertion is the 1903 arbitration of the Alaska Boundary Dispute. The dispute arose over, as the name suggests, the Alaskan border; specifically the question was whether the Yukon Territory (which was in the middle of a gold rush) could have access to the Pacific Ocean.

I'd love it if someone could fill in more detail but the end result of the dispute was arbitration as per the Hay-Herbert Treaty. The tribunal that heard the American and Canadian cases was composed of three Americans, two Canadians, and a Brit (Baron Alverstone). Ultimately Alverstone sided with the Americans, which inspired major suspicion of the British throughout Canada. It's important again to highlight that this is both an Anglo and a French phenomenon, which makes it distinct from prior Canadian nationalist sentiments which took either a linguistic turn (i.e.: the Québécois) or were pro-British imperial sentiments.

While it's important to note that anger towards the British was more pronounced in the Dominion than anger towards the United States, Canada remained skeptical of Americans. Indeed, the so-called reciprocity election of 1911 focused primarily around Canada's economic relationship with the United States and resulted in Canada rejecting closer economic ties with the US and indeed ended the rule of Wilfred Laurier.

Recalling that Canada is limited at this point in history as to how much formal diplomatic activity it could engage in without formally relying on the British, Canada/US relations were from the Canadian side largely concerned with the amount of power America should have over Canada vis-á-vis the British Empire. To an extent this remains a classic problem in Canadian politics - it's worth noting that most eras of Canadian political thought have major texts (George Grant's "Lament for a Nation" and Harold Innis' "the Fur Trade in Canada" come to mind as two texts struggling with Canada/US and Canada/Imperial relations respectively) that expressly struggle with this dynamic and its implications.

Anyone who can fill in more detail would be much appreciated. I'm running on my undergraduate Canadian history lectures to write this.